Chromecast: add platform hooks to inject browser/renderer message filters.

chromecast/renderer/cast_content_renderer_client.h

Index: chromecast/renderer/cast_content_renderer_client.h
diff --git a/chromecast/renderer/cast_content_renderer_client.h b/chromecast/renderer/cast_content_renderer_client.h
index 9f0dfbdb116c165f3a4b9c47a996ff4e5c9e0b2a..c41b98d6be82492efff3018140c3969b380adfd0 100644
--- a/chromecast/renderer/cast_content_renderer_client.h
+++ b/chromecast/renderer/cast_content_renderer_client.h
@@ -10,6 +10,10 @@
 #include "base/macros.h"
 #include "content/public/renderer/content_renderer_client.h"
 
+namespace IPC {
+class MessageFilter;
+}
+
 namespace network_hints {
 class PrescientNetworkingDispatcher;
 }  // namespace network_hints
@@ -18,6 +22,7 @@ namespace chromecast {
 namespace shell {
 class CastRenderProcessObserver;
 
+// Adds any platform-specific bindings to the current frame.
 void PlatformAddRendererNativeBindings(blink::WebLocalFrame* frame);
 
 class CastContentRendererClient : public content::ContentRendererClient {
@@ -25,6 +30,11 @@ class CastContentRendererClient : public content::ContentRendererClient {
   CastContentRendererClient();
   ~CastContentRendererClient() override;
 
+  // Returns any MessageFilters from the platform implementation that should
+  // be added to the render process.
+  std::vector<scoped_refptr<IPC::MessageFilter>>
+  PlatformGetRendererMessageFilters();
+
   // ContentRendererClient implementation:
   void RenderThreadStarted() override;
   void RenderViewCreated(content::RenderView* render_view) override;